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HCN is the putative product of C-1 and amino moieties of 1-aminocyclopropane-l-carboxylic acid (ACC) during its conversion to ethylene.In apple (Malus sylvestrus Mill.) slices or auxin-treated mungbean (Vigna radiata L.) hypocotyls, which produced ethylene at high rates, the steady state concentration of HCN was found to be no higher than 0.2 micromolar, which was too low to inhibit respiration (reported Ki for HCN to inhibit respiration was 10-20 micromolar). However, these tissues became cyanogenic when treated with ACC, the precursor of ethylene, and with 2-aminoxyacetic acid, which inhibits 6-cyanoalanine synthase, the main enzyme to detoxify HCN; the HCN levels in these tissues went up to 1.7 and 8.1 micromolar, respectively. Although ethylene production by avocado (Persea gratissima) and apple fruits increased several hundred-fold during ripening, f-cyanoalanine synthase activity increased only one-to two-fold. These findings support the notion that HCN is a co-product of ethylene biosynthesis and that the plant tissues possess ample capacity to detoxify HCN formed during ethylene biosynthesis so that the concentration of HCN in plant tissues is kept at a low level.Plant hormone ethylene is produced by all plants and in trace amounts elicits many physiological responses. Ethylene is biosynthesized in plants via the following sequence: methionine -* S-adenosylmethionine --+1 -aminocyclopropane-1 -carboxylic acid --C2H4 (19). In the biological oxidation of ACC2 to ethylene, it has been shown that carboxyl carbon, C-1, and C-2,3 of ACC are metabolized into C02, ,3-cyanoalanine derivatives, and ethylene, respectively (11,12). Although no free HCN was identified, it was asserted that C-1 of ACC is initially liberated as HCN but is rapidly conjugated into ,B-cyanoalanine derivatives as soon as it is liberated. This notion was based on the observation that the metabolic fate of the C-1 of ACC during its conversion to ethylene was identical to that of administered HCN and that the amount of HCN-conjugates formed was equivalent to that of ethylene produced (1 1 (3-cyanoalanine) ,-Cyanoalanine synthase is widely distributed in higher plants (9). ,3-Cyanoalanine thus formed is further metabolized to asparagine or to y-glutamyl-,3-cyanoalanine (1-4, 6, 9, 11, 12 MATERIALS AND METHODS Plant Materials. Apple (Malus sylvestrus Mill., var Golden Delicious) slices (1 cm in diameter, 0.5 cm in length) were prepared from fruits harvested from a local orchard and stored at 0°C. Avocado (Persea gratissima) were purchased from the local market. Mungbean ( Vigna radiata L.) hypocotyl segments (2 cm long) were prepared from 3-d-old etiolated seedlings grown at 25°C.Incubation Conditions. Apple slices were presoaked in 2% KCI solution containing specified chemicals in a 50-mL flask for 2 h, blotted dry, and then incubated at 25°C in a 10-mL flask sealed with a serum cap. Each flask contained a plastic center well with 200 gL of 0.1 N NaOH to trap the released HCN. Mungbean hypocotyls were similarly treated as apple slices ...

Degenerate oligonucleotide primers corresponding to conserved regions flanking the active-site domain of 1-aminocyclopropane-l-carboxylate (ACC) synthase (EC 4.4.1.14) were used for the polymerase chain reaction (PCR) to amplify DNA fragments from mRNA isolated from tomato fruit and tomato suspension cell culture. Antibodies raised against two conserved peptide sequences (TNPSNPLGTT and SLSKDLGLPGFRVG) were used to screen for positive colonies, after the PCR products were cloned into a Bluescript plasmid and expressed in Escherichia coli. Four distinct cDNA fragments encoding ACC synthase homologs were isolated. While pBTAS1 and pBTAS4 were obtained from fruit mRNA, cell culture mRNA yielded three sequences, pBTAS1, pBTAS2, and pBTAS3. Sequencing ofthese gene fragments revealed that pBTAS1 and pBTAS4 were identical to those full-length sequences previously reported by Van Der Straeten et al. [Van

The pyridoxal phosphate (PLP)-dependent 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (S-adenosyl-L-methionine methylthioadenosine-lyase, EC 4.4.1.14), the key enzyme in ethylene biosynthesis, is inactivated by its substrate S-adenosylmethionine (AdoMet). Apple ACC synthase was purified with an immunoaffinity gel, and its active site was probed with NaB3H4 or Ado[(4C]Met. HPLC separation of the trypsin digest yielded a single radioactive peptide. Peptide sequencing of both 3H-and 14C-labeled peptides revealed a common dodecapeptide of Ser-Leu-Ser-Xaa-Asp-Leu-Gly-LeuPro-Gly-Phe-Arg, where Xaa was the modified, radioactive residue in each case. Acid hydrolysis of the 3H-labeled enzyme released radioactive N-pyridoxyllysine, indicating that the active-site peptide contained lysine at position 4. Mass spectrometry of the "4C-labeled peptide indicated a protonated molecular ion at m/z 1390.6, from which the mass of Xaa was calculated to be 229, a number that is equivalent to the mass of a lysine residue alkylated by the 2-aminobutyrate portion of AdoMet, as we previously proposed. These results indicate that the same active-site lysine binds the PLP and convalently links to the 2-aminobutyrate portion of AdoMet during inactivation. The active site of tomato ACC synthase was probed in the same manner with Ado [14C]Met. Sequencing of the tomato active-site peptide revealed two highly conserved dodecapeptides; the minor peptide possessed a sequence identical to that of the apple enzyme, whereas the major peptide differed from the minor peptide in that methionine replaced leucine at position 6.The plant hormone ethylene regulates many aspects of plant growth and development. Adams and Yang (1) have established that ethylene is biosynthesized via the following se-

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Background and objective Airway inflammation accompanying exacerbations varies among individuals with some having neutrophilic, while others showing eosinophilic inflammation. This study assessed the cut‐off values of blood eosinophil count for identifying subjects with longer hospital length of stay (LOS) with acute exacerbations of chronic obstructive pulmonary disease (AECOPD). Methods Patients were recruited at presentation to the hospital with an AECOPD. Complete blood picture with differential count was taken on admission. Patients were treated with a standard course of systemic corticosteroid and antibiotic and evaluated at 8 weeks post‐exacerbation for lung function measurement and 6‐min walk. They were followed up in 1 year for any readmissions or mortality. Cut‐off values of eosinophils for assessment of longer LOS were calculated using receiver operating characteristic (ROC) curve analysis. Results A total of 346 patients with admission eosinophil count were included in the analysis (333 (96.2%) were males; mean ± SD age: 74.9 ± 7.8 years; mean forced expiratory volume in 1 s (FEV1): 43.4 ± 16.3% predicted). The median (interquartile range (IQR)) of the absolute peripheral eosinophil count, percent eosinophil count and LOS were 0.11 (0.25) × 109/L, 1 (3) % and 5 (7) days, respectively. Using the median LOS of ≥5 days as the cut‐off, ROC analysis of the cut‐off value of eosinophil count associated with longer LOS was at <2% (area under the curve (AUC): 0.666, P < 0.001) while absolute eosinophil count was at <0.144 × 109/L (AUC: 0.645, P < 0.001). These eosinophil cut‐off values could predict longer LOS independent of age, lung function and previous hospital admissions, but had no association with readmissions for AECOPD and mortality at 12 months. Conclusion An eosinophil value of <0.144 × 109/L on admission or <2% was associated with longer hospital LOS for AECOPD.

Cytokinins are known to stimulate ethylene production in mungbean hypocotyls synergistically with indoleacetic acid (IAA), in mungbean hypocotyls synergistically with Ca2", and in wilted wheat leaves. Thidiazuron, a substituted urea compound, mimicked the effect of benzyladenine (BA) in all three systems. In the Ca2" + cytokinin system and the IAA + cytokinin systems of mungbean hypocotyls, thiadiazuron was slightly more active than BA at equimolar concentration. In mungbean hypocotyls exogenously applied IAA was rapidly conjugated into IAA asparate, and this conjugation process was effectively inhibited by thidiazuron, as by cytokinins. In the wilted wheat leaves system, 10 micromolar thidiazuron exerted stress ethylene production equal to that exerted by 1 millimolar BA, indicating that thidiazuron is more active than BA by two orders. The structure-activity relationship of thidiazuron and its thiadiazolylurea analogs in stimulating Ca2+-dependent ethylene production in mungbean hypocotyls was found to agree well with the structureactivity relationship of these derivatives in promoting the growth of callus tissues. These results indicate that thidiazuron and its derivatives are highly active to mimic the adenine-type cytokinin responses in promoting ethylene production and that the structure-activity relationship in promoting the growth of callus and in promoting ethylene production is similar.